This invention relates to a process for preparing 2-carboxyalkyl(aryl)phosphinic acid and its corresponding anhydride(s). More specifically, this invention relates to a process for preparing 2-carboxyethyl(aryl)phosphinic acid using an improved hydrolysis process for intermediates involved in the overall reaction. In particular, this invention relates to a process for preparing 2-carboxyethyl(phenyl)phosphinic acid and its cyclic anhydride.
2-Carboxyethyl(phenyl)phosphinic acid, useful as a flame retardant additive for polymers such as polyesters and polyamides, has been prepared by reacting acrylic acid with dichloro(phenyl)phosphine in a reaction mixture. This reaction mixture was subjected to a separate hydrolysis step to obtain the desired product: 2-carboxyethyl(phenyl)phosphinic acid.
2-Carboxyethyl(aryl)phosphinic acid and its cyclic anhydride are useful as flame retardant additives for polymers such as polyesters, polyamides and the like.
U.S. Pat. No.5,334,760 which issued on Aug. 2, 1994, to Toshio Wachi et al. (hereinafter xe2x80x9cthe ""760 patentxe2x80x9d) discloses a process in which acrylic acid or methacrylic acid is reacted with dichloro(phenyl)phosphine in the presence of a catalyst (Column 1, lines 51-68). That reaction product is hydrolyzed as the ""760 patent subsequently discloses:
With the reaction product wherein water is added at a molar amount of 5 to 20 times of the reaction product or with the reaction product dropped in water having the same molar amount as the above, a reaction is carried out at a temperature of 0xc2x0 to 100xc2x0 C. for 1 to 3 hours. After completion of the reaction, the resulting reaction product is cooled under stirring, so that a crystal is deposited. (Column 4, line 62-Column 5, line 1).
The ""760 patent is incorporated herein in its entirety by reference.
U.S. Pat. No. 4,081,463 which issued to Birum et al. on Mar. 28, 1978 (hereinafter the xe2x80x9c463 patentxe2x80x9d) discloses, at column 1, lines 21-25, a process in which a 25-45% molar excess of acrylic acid was used in a reaction of acrylic acid with dichloro(phenyl)phosphine. The ""463 patent is incorporated herein in its entirety by reference. For the hydrolysis step, the ""463 patent discloses adding the undiluted reaction product of acrylic acid and dichloro(phenyl)phosphine to at least enough water to complete hydrolysis, with it being reportedly advantageous to use a significant excess of water to aid stirring and temperature control. Use of a 5 to 15 molar excess of water is taught at column 1, lines 58-60, as being convenient. This molar excess of water is equivalent to conducting the hydrolysis reported in this patent using 12 to 32 moles water per mole of dichloro(phenyl)phosphine charged to the reaction of acrylic acid with dichloro(phenyl)phosphine.
U.S. Pat. No. 4,769,182 which issued to James R. Hazen on Sep. 6, 1988, (hereinafter the xe2x80x9c""182 patentxe2x80x9d) discloses at column 2, lines 30-38, a process in which a 0-20% molar excess of acrylic acid was used in the reaction of acrylic acid with dichloro(phenyl)phosphine. The ""182 patent is incorporated herein by reference in its entirety. In its hydrolysis step, the ""182 patent discloses that typical hydrolysis conditions for acid chlorides and similar water-reactive species are used, with a xe2x80x9cdrowningxe2x80x9d technique being preferred, see column 4 lines 45-48. This xe2x80x9cdrowningxe2x80x9d technique involves the use of significant excess water, i.e. 25.7 moles water per mole of dichloro(phenyl)phosphine charged to the reaction of acrylic acid with dichloro(phenyl)phosphine. Conducting the hydrolysis in this manner reportedly produces 2-carboxyethyl(phenyl)phosphinic acid as a white microcrystalline powder. However, by avoiding a solid phase and driving off hydrogen halides (e.g. HCl) to improve crystal size, the instant invention produces a purer product with less net trapped impurities.
It is desirable to produce 2-carboxyalkyl(aryl)phosphinic acid with improved product recovery and washing, resulting in improved product quality. This improved quality provides a 2-carboxyalkyl(aryl)phosphinic acid product for use in a polymerization process producing a flame retardant polymer with better color quality, lower catalyst losses in such process, and less corrosion of processing and handling equipment.
It has now been discovered that conducting the hydrolysis with significantly less water present than taught or suggested by the prior art produces 2-carboxyalkyl(aryl)phosphinic acid having enhanced filterability, washing and flowability properties along with a higher bulk density. Enhanced filterability lowers process cycle times and increases productivity.
It has been unexpectedly discovered that the controlled water addition of the process of this invention to the reaction composition avoids a premature solid phase.
Further, it has been discovered herein that by adding water to the reaction composition according to the process of the instant invention, that hydrogen halide (e.g. HCl) is given off in larger than expected quantities, allowing for the formation of larger, more durable crystal size, which improves the resultant product purity, washing, drying, and filterability.
It is an object of the invention to provide a process for producing 2-carboxyalkyl(aryl)phosphinic acid having improved filterability.
It is a further object of this invention to provide a process to produce 2-carboxyalkyl(aryl)phosphinic acid having lower levels of impurities.
It is a still further object of the invention to provide a process for producing 2-carboxyalkyl(aryl)phosphinic acid which results in improved product washing, faster filtration and better flowability of the final product, each of which can aid in facilitating and enhancing packaging of 2-carboxyalkyl(aryl)phosphinic acid of this invention.
It is yet a further object of the invention to provide a process for producing 2-carboxyalkyl(aryl)phosphinic acid which enables hydrogen halide produced (e.g. HCl) during the hydrolysis reaction to be removed prior to recovery of 2-carboxyalkyl(aryl)phosphinic acid from the hydrolysis reaction mixture, thereby lowering the level of halide in the final product and enhancing 2-carboxyalkyl(aryl)phosphinic acid crystal size (lower levels of halide minimizes corrosion of metal equipment in uses of 2-carboxyalkyl(aryl)phosphinic acid such as in polymer applications).
It is another object of this invention to avoid an unstirrable or difficult to stir solid in a reaction producing 2-carboxyalkyl(aryl)phosphinic acid for an easier and safer process.
It is an additional object of this invention to provide a process to produce an anhydride corresponding to 2-carboxyalkyl(aryl)phosphinic acid.
These and other objects are achieved in the process of this invention which is described in more non-limiting detail hereinafter.
The invention comprises a process for producing 2-carboxyalkyl(aryl)phosphinic acid, wherein aryl is phenyl or C1-C4 alkyl substituted phenyl, comprising adding water to a first reaction mixture comprising the products of the reaction of dihalogenated (aryl)phosphine and a carboxylic acid selected from acrylic acid or methacrylic acid, and hydrolyzing said reaction products to produce a second reaction mixture comprising a corresponding 2-carboxyalkyl(aryl)phosphinic acid; wherein water is added at a controlled rate to said first reaction mixture and the temperature is controlled to maintain the reactor contents in a stirrable state, and wherein the temperature is at least about 125xc2x0 C. before the end of the hydrolysis reaction.
This invention also comprises a process for producing 2-carboxyalkyl(aryl)phosphinic acid, wherein aryl is phenyl or C1-C4 alkyl substituted phenyl, comprising adding water to a first reaction mixture comprising the products of the reaction of dihalogenated (aryl)phosphine and a carboxylic acid selected from acrylic acid or methacrylic acid, and hydrolyzing said reaction products to produce a second reaction mixture comprising 2-carboxyalkyl(aryl)phosphinic acid, and simultaneously removing at least a portion of the hydrogen halide present during the hydrolysis reaction, wherein water is added at a controlled rate to said first reaction mixture to enable removal of at least about 35% of the theoretically available halogen in said first reaction mixture during the hydrolysis, and wherein the temperature at the end of th e hydrolysis reaction is at least 125xc2x0 C.
In an embodiment of these processes, the temperature after addition of two moles water per mole dihalogenated (aryl)phosphine charged to the reaction between dihalogenated (aryl)phosphine and carboxylic acid is at least 125xc2x0 C.
This invention also comprises a process for producing 2-carboxyalkyl(aryl)phosphinic acid cyclic anhydride(s) comprising adding water to a first reaction mixture comprising the products of the reaction of dihalogenated (aryl)phosphine, wherein aryl is phenyl or C1-C4 alkyl substituted phenyl, and a carboxylic acid selected from acrylic acid or methacrylic acid, and hydrolyzing said reaction products to produce a second reaction mixture comprising a corresponding 2-carboxyalkyl(aryl)phosphinic acid cyclic anhydride; wherein up to about one mole water per mole of dihalogenated (aryl)phosphine is added at a controlled rate to said first reaction mixture and the temperature is controlled to maintain the reactor contents in a stirrable state, and wherein the temperature after addition of water is at least 75xc2x0 C.
As with an above described process for producing the 2-carboxyalkyl(aryl)phosphinic acid, the reaction producing 2-carboxyalkyl(aryl)phosphinic acid cyclic anhydride comprises simultaneously removing at least a portion of available hydrogen halide during the hydrolysis reaction. The controlled addition of one mole water or less per mole of dihalogenated (aryl)phosphine charged to the reaction enables the removal of at least about 35% of the theoretically available halogen in said first reaction mixture during the hydrolysis.
The corresponding cyclic anhydride, besides being an important intermediate in the process of the instant invention to produce 2-carboxyalkyl(aryl)phosphinic acid, has other uses such as replacing 2-carboxyalkyl(aryl)phospinic acid, as a reactant in chemical reactions (due to the higher reactivity of the cyclic anhydride).